Clamping fixture



1945 E. F. HOHWART 2,370,351

CLAMPING FIXTURE Original Fi l-ed March 19, 1943 3 Sheeizs-Sheet 1 INVEN TOR A TTORNE Y6.

Feb. 27, 1945; E F, HOHWART 2,370,351

CLAMIZ'ING FIXTURE 3 Sheets-Sheet 2 Original Filed March 19, 1943INVENTOR 291,852 F/Vo/Iurarif Feb. 27, 1945. HQHWART 2,370,351

CLAMPING FIXTURE Original Filed March 19, 1943 s Sheets-Sheet s PatentedFeb. 27, 194-5 UNITED STATES PATENT OFFICE CLAMPING FIXTURE Q Ernest F.'Hohwart, Detroit, Mich., assignor to N. A. WoodworthCompany,;Ferndale,Mich., a

corporation of Michigan "Continuation of application Serial No. 479;714,

March '19, 1943.

This application April 28, I

1943, Serial No. 484,859-

10 vClaims.

tively 'movable parts together with means for moving the parts towardand from one another and automatically operable t lock the parts againstinadvertent retractable movement when the desired clamping pressure isapplied to the piece of work confined between them; the provision of astructure as above described in'whic'h the locking means comprisesa'pair of parts having surface engagement with respect to each other;the provision of a structure as above 'described in which such surfaceengagement is of a relatively great extent as compared to structuresheretofore proposed; the provision of a structure as above described inwhich such surface engagement is of a relatively great extent ascompared to structures heretofore proposed; the provision of a structureas above described in which'the relatively movable parts areautomatically locked against inadvertent movement both when in clampingrelation with respect to each other and when separated from each otherto receive apiece of work between them; and the provision of a device ofthe type described so constructed and arranged as to lock therelativelymovable parts against inadvertent'mo-vement in atieastonedirection upon the application of lpressure in the direction of movementthereof, that is of .extremely simple, durable and economical construc-'tion involving a minimum of parts.

Other objects of the inventioninclude the provision of a clampingfixture comprising a base and a clamping member relativelymovable withrespect thereto, a post extending between the base and the clampingmember and having rack teeth formed thereon, a shaft part 'rotatablymounted in the base and having a pinion part thereon arranged in meshingrelationship with respect to the rack teeth on the post, the shaft partbeing rotatable whereby to act through the pinion part and the rackteeth to cause the clamping member to approach toward or recede from thebase, a handle or wrench part to turn the and provided with "a frictionsurface thereon arranged for frictional engagement with a complementarysurface -of said base upon said axial shifting thereof inone direction,the connection between said wrench-part-andsaid post includingcooperating force transmitting surfaces "inclined with respect to thedirection of force exerted therebetween whereby to be effective to urgethe axially shfftable part axially thereof 'upon "the 10 transmission ofsuchiforce between them to effect frictional engagement of said"frictional surfaces, thereby to lock said clamping member againstinadvertent movement with respect to said base; the provision of aconstruction as above de- 5 scribed in which the shaft part and thepinion part are fixed with respect to'each other and the "pinion isprovided with helical teeth cooperating with complementary formed teethon the post constituting theinclined surfaces urging the shaft partandthe pinion part axially during a clamping operation; the provisionofta construction as first above mentioned in which the pinion part isaxially shiftable upon theshaftpart; the provisionof a construction-aslast described in'which 2c the pinion part is provided with helicalteeth lying in meshing relationship with complementary teeth formed onthe post whereby the pinion is urged axially 'under the force of aclamping operation; and the provision of any one of the '3 structuresabove described in whichthe frictional surfaces providing the clampingeffect between the base andone of the parts are con'icalsurfaces.Further objects ofthe invention include the provision of aclampingfixture asabove described in which the clamping memberisfrictionally locked against movement in either direction upon thepresence of a force tending to restrict its movement in such direction;the provision of a construction as above described in which theoperating shaft may be inserted "from eithertend of the opening providedtherefor in the base whereby it may be employed either as .a righthandor a left-hand fixture; the provision of a construction as abovedescribed in which a yielding connection is provided between-theoperating post and the clamping member; and the provision of aconstruction as above described in which movement of the clamping memberwith respect to the base is guided-independently of the means forefiecting movement between the clamping member and the base.

The above being among the objects of the present invention the sameconsists in certain "novel shaft, one of said parts being axiallyshiftable 5o *"feaitures of construction and combinations of parts to behereinafter described with reference to the accompanying drawings, andthen claimed, having the above and other objects in view.

In the accompanying drawings which illustrate suitable embodiments ofthe present invention and in which like numerals refer to like partsthroughout the several difl'erent views,

Fig. l is a partially broken, partially sectioned front elevational viewof a two-post clamping fixture constructed in accordance with thepresent invention;

Fig. 2 is a partially broken plan view of the clamping fixture shown inFig. 1;

Fig. 3 is a transverse sectional view taken on the line 3-3 of Fig. 1;

Fig. 4 is a fragmentary elevational view taken from the opposite side ofthe fixture from the view shown in Fig. 1 and illustrating thecooperating portions of one of the posts and the associated portion ofthe operating shaft to better illustrate the arrangement ofthecooperating gear teeth thereon;

Fig. 5 is an end elevational view of the clamp ing fixture shown in-thepreceding views;

Fig. 6 is a transverse sectional view taken on the line 6-6 of Fig. 1;

Fig. '7 is a fragmentary, sectional view taken centrally through theoperating shaft of a modified form of construction in which the conelocking elements are formed at the opposite end of the operating shaftfrom that illustrated in the preceding figures;

Fig. 8 is an end elevational view of the construction shown in Fig. '7,taken from the lefthand end thereof;

Fig. 9 is a view similar to Fig. '7 but illustrating a modified form oflocking cone arrangement at the same end of the operating shaft;

Fig. 10 is a fragmentary, partially broken, partially sectioned viewillustrating a modified form of construction of the inter-engaging conelooking surfaces at the same end of the shaft as such surfaces arelocated in Fig. 1;

Fig. 11 is a view similar to Fig. 10 but illustrating a further modifiedform of construction for the cooperating cone locking surfaces;

Fig. 12 is a partially broken, partially sectioned plan view similar toFig. 2 illustrating another modified form of construction;

Fig. 13 is-a partially broken, partially sectioned front elevationalview of the construction shown in Fig. 12;

Fig. 14 is a fragmentary partially broken, partially sectionedelevational view illustrating a modified form of connection between theposts and the clamping plate where it is desired to introduceyieldability into such connection;

Figs. 15 and 16 are fragmentary, partially broken, partially sectioned'views illustrating modified forms of handle or wrench construction forthe operating shaft; and

Fig. 17 is a fragmentary, vertical, sectional view illustrating amodified clamping structure in which the pinion is movable axially ofthe operating shaft and the operating shaft is held against axialmovement.

The present invention relates to that class of devices commonly known inshop practice as clamping fixtures and which are employed in machineshops and the like to clamp a piece of work therein for the purpose ofholding and locating such work during a machining operation thereon. Itfurther relates to that type of such clamping fixtures as are providedwith means for automatically locking the two parts thereof between whichthe work is clamped against inadvertent separation from one another whena suitable clamping force has been applied to the work positionedbetween them. v

Such clamping fixtures conventionally comprise a base in which one ormore posts are axially slidably received, such post or posts carrying aclamping member or a plate thereon and which plate member is therebymovable toward and from the base in order to clamp a piece of workbetween it and the base. In order to effect movement between theclamping plate and the base it is conventional practice to form the postor posts with rack teeth thereon and to provide a shaft rotatablymounted in the base at right angles to the post and to provide suchshaft with gear teeth thereon in mesh with the rack or racks on the postor posts so that by rotating the shaft the post or posts andconsequently the clamping plate may be moved toward or from clampingposition with respect to the base. i

It is desirable to provide means in conjunction with such clampingfixtures so that when the shaft is operated to clamp a piece of workbetween the plate and the base and a sufficient amount of clamping forcehas been exerted on the work to hold it tightly in place for the purposeof the subsequent machining operation thereon, the shaft will beautomatically locked against inadvertent reversal of movement so thatsuch clamping force is maintained until it is desired to release thework. In the past the forms of construction employed for so locking theshaft against rotation have been more or less in the form ofconventional one-way or over-running clutches and so constructed andarranged that a reversal of the turning force applied on the shaft toclamp the work in the fixture will release the clutch and permit theshaft to be rotated in a reverse direction in order to release the pieceof work from the fixture. The form of locking means heretofore providedhas been such, because of the use of balls or rollers as wedging meansbetween a pair of relatively movable surfaces, that when a large numberof parts of substantially the same size are clamped one after the otherin the same fixture, the wedgin means are repeatedly clamped between therelatively movable parts at substantially the same location in each caseand eventually become imbedded or form a depression at the point ofmaximum pressure, an occurrence commonly known as Brinelling in theindustry, with the result that such wedging means become ineffective orat least inefficient at such location and replacement or repair of thelocking means, therefore, becomes necessary. Additionally, the form oflocking means heretofore employed has usually required the use of anumber of separately formed parts each requiring a relatively highdegree of accuracy in their manufacture and, therefore, requiring amaterial amount of expense in providing them.

The present invention provides a construction wherein all of theadvantages of the prior art clamping fixtures including the self-lockingfeatures thereof are provided while eliminating the disadvantageousfeatures thereof, materially reducing the cost of the same and thelocking feature of which is of extremely simple construction whicheliminates to a great extent the high degree of accuracy in manufacturenecessary in prior constructions. Furthermore, instead of providingpoint or line contact between the relatively movable parts of thelocking device, surface contact is. provided so that the possibility ofasz rm reducing the :efiiciency vroffiifne locking device throughBrinelling of thef lock elements .isldefinitely avoided. illhe present:invention, therefore,

provides :a :structure "which "is at least as efiective as the priorsart structures, 'is considerably more economical to :build, .has almostunlimited life, and is extremely simple in construction endinvolves aminimum number of parts.

The above advantages are obtained accord- ;ance with the present'inventionzin an extremely simple manner :by so fomn'mg "the teeth ofthe pinion .=and the rack-on'the post that .the application of aclamping :force between the pinion and the rack willshi'ft the pinionaxially to draw a pair of "irictionalflocking:surfacesintotrictional llocking engagement withaeach'other. 'Thisefiect is obtained in a simplemanner :by employing .a pinion with helical teeth and employing:c'omp'lementary rack teeth 0n the :post which :automatically provides aconstruction in which the engaging surfaces between (the :pinion and thepost are inclined with respect to the direction of the force transmittedthrough them :and conseouently tends'to axiallyshiit the pinion fromsitsnormal position whenever a material :force is transmitted between thepinion and the rack on the post tending to move the :post againstresistanoe. The pinion is, of course'mountea for a limited amountofaXia'l movement in the "base and :is provided with an :associatedfriction :surface for frictional locking engagement with acomplementarysurface formed on'the'base. As

previously stated, such 'friction surface is preferably in the form of aconical or frusto con'ical surface and in this case concentric 'withtheaxis of rotation of the pinion. Thus whenever the operating shaft isturnedtoeffect the clamping of a piece of work between the clampingplate and the base, the application of a turning force on the shaft toeffect the desired clamping presrelation of the inter-engaging teeth ofthe "pinion and rack relative to the axis of the pinion, immediatelytend to separate the conical surfaces and thereby free the shaft andpermit it to be rotated in a reverse direction without substantialresistance. It will, therefore'lee appreciated that by this simpleexpedienta highly efiicient andextremely economical self-locking featureis provided in'suchclamping fixture.

Referring now to the accompanying drawings and particularly'to Figs. 11306 inclusiveQin which one form of the last-described typeof-'construction is shown, it will be seen 'to include a base '20provided with a raised central portion 2 2'131'0- ividing awork-receiving portion or table. Lo-

cated vertically above the base 20 and table 22 is a so-called clampingplate vertically movable toward and from the table portion '22 in orderto enable a piece of work, here indicated more or less diagrammaticallyat '26 between them. "It will be understood that in actual practicethese clamping fixtures are employed to hold a large 1? number of parts,one after the other, for some machining operation thereon and that thetable 22 and the plate 24 may have their opposed faces of suitableconfiguration for 'interengagem'ent with "a workpiece 'so as to locatethe workpiece :a predetermined :relation with rrmpect thereto and;further :that the zplate member-2'4 :may, :for --instance,rhe'proridedwithsuitable drill bushings -(not shown) :therein xiorlocating "a drill or the like which to operate upon the work.atrarpredetermined ep'osition on the work thus ;.located .in "theclamping tfixture. Matters :of this zcharacter .-.are well understood:by :those skilled .in the art ;-and=require.no;iurther explanation.

In order :to :connectthe clamping plate .24 with the base 20such-clamping:fixturesconventionally employ one or more posts extendingbetween them, fixed 'to one, usually the plate :24, and 'slidablyreceived by the other, usually the :base .20. Most 10f such fixturesemploy two of such 'postsrand, .according'1y,two such .posts 128 areJil- "lustrated :in the :fixtures :s'hown in the accompanyingdrawings-which posts are shouldered as at 30 :for engagement with thebottom "face 'of'the :plate :24 and project upwardly therethrough and"above the clamping plate are provided with 'nuts v32 threaded thereonand which serve as :means for rigidly clamping the plate '24 inengagement with the shoulders 639. The clamping :plate '24 is preferablyprovided with a :boss such as "34 around theupper end of .eachpos't'28and aweb 38 interconnecting'thezbosses so as to renderthe clamping plate24 as rigidas possible. Thetbase 1213 :is provided with a :pairofupstanding bosses 33 in which the lower portions of the :posts 28 areverti'callyfisli'dablynreceived,"thelbosses 38 preferably beingofamaterial "height so as to provide .an'amp'lebearing surface fortheposts28 in their sliding movement'therein.

The base '20 is provided withapair of horizontally-directed alignedbearin bosses 4;! formed integrally therewith, each centrally disposedtransversely with respect to-the corresponding one of the bosses 38 andaxially offset' from such bosses :as indicated. A shaft 82 extendbetween and projects through both of the'bearing bosses it and 'isrotatably received therein. The shaft 3-2 has rigidly fixed thereto,and'preferably formed integrally therewith as shown, a pair of pinions4'4 each of which is centrall disposed transversely with respectto acorresponding one of the posts 28. Each post .28 is formed 'to-provide-on--that face thereof opposed to the corresponding of such pinions arack 46 the teeth of which lie in meshing relationship with respect tothe corresponding of such pinions M, so that basically the structure asthus far described is similar to the prior artconstructions in thatrotation of the shaft :42 acting through the pin- ,ions '44 and racks 4Eacts to raise or 'lower the Q513 28, dependingupon the direction ofrotation of the shaft t2, and consequently cause the clampin plate '35to approach toward or recede from the upper 'face of the table portionJ22 of the base 23. Any-suitablemeans may be provided for turning theshaft 42, the particular means "s'how-n in-thedrawings by wayiofillustrationcomprisin .wrenchor lever-"All nonrotatably'secured to oneoutwardly projecting-end of the shaft M and terminating at its outerfree end in anoutwardl-y offset bal1 58 capable of being readily graspedby a workman and operated to efiect rotation of the shaft 6'2.

in accordance with the present invention and where the type ofconstruction shownin Figs. 1 to 1'3 is-emplo-yed, then, as 'best'brought out'in Fig. 4, at least one of the-pinions '44 and itscorresponding rack 4'6, instead of being of the straight spur-gear type'as is "employed in prior Lart devices of this character, is of a helicalgear type. As will hereinafter be more apparent, while the principles ofthe present invention may be realized in a multi-post clamping fixtureby utilizing only one such spiral pinion between the operating shaft andone post only, and employing straight spur gears between the operatingshaft and the remaining posts, it is preferable that all of the pinionsbe of the helical type and such structure is shown by way ofillustration. Where more than one helical pinion is employed and all arerigidly fixed to the operating shaft, it will be appreciated from thefollowing description that all of th pinions must be of the same handwhen located on the same sides of the posts; that is, the teeth of allof them should turn in the same direction about the axis of theoperating shaft and all are preferably spiraled in the same degree aboutthe axis of the operating shaft. The amount of spiral, that is thedegree to which the teeth are spiraled, measured by a line tangent tothe pitch line of the teeth and its relation to the axis of the shaftmay vary to a greater or lesser degree, depending upon the type andcharacter of the friction surfaces employed in conjunction therewith aswill be readily appreciated. In other words, any suitable angle may beemployed as long as it is sufiicient to provide the necessary axialforce on the operating shaft during a clamping operation as willhereinafter be more fully explained, and is more or less interrelatedwith the angularity of the coned surfaces where employed as the frictionsurfaces as will hereinafter be more apparent. However, it may be statedthat an angularity of the teeth of the pinions 44 of approximately 45degrees to the axis of the shaft has proven satisfactory in servicewhere coned friction surface of the type shown are employed inconjunction therewith.

Referring now to Fig. 4 which particularly brings out theinter-engagement of the teeth of one of the pinions 44 on the operatingshaft 42 with the teeth of the rack 45 on the corresponding post 28, itwill be appreciated that as the shaft 42 is turned to lower the post 28and consequently the clamping plate 24 to clamp -a piece of work such as26 between the clamping plate 24 and the table 22, as soon as the plate24 contacts the upper face of the workpiece 26, further downwardmovement of the clamping plate 24 and consequently the post 28 will beprevented. At this point, of course, a relatively heavy pressure isapplied to the handle or lever 48 to securely clamp the work in place asthis pressure is applied to the shaft 42 attempting to cause furtherrotation thereof under such circumstances, such force or pressure inbeing transmitted from the teeth of the pinion 44 to the teeth of therack 48 will, because of the angularlty of the teeth of the pinion andrack, set up a component of force axially of the shaft 42 tending to movsuch shaft axially thereof relative to the base 20, such force beingdirectly proportional to the turning force applied to the shaft 42 andthe proportional amount of such turning force exerted axially of theshaft depending upon the angle of the teeth of the pinion and rack withrespect to the axis of the shaft 42. The amount of axial force in theshaft 42 occurring during normal raising and lowering movement of theclamping plate 24 and before any clamping force is actually applied tothe work received by the fixture is relatively small because of therelatively small turning force necessarily applied to the shaft in somoving the clamping plate 24, a material axial force of the shaft 42occurring under the above-described conditions only when a materialresistance is offered to movement of the clamping plate 24 and/or post28.

In accordance with the present invention advantage is taken of the axialforce exerted on the shaft 42 upon the occurrence of a materialresistance offered to vertical movement of the clamping plate 24 andpost 28 as above described to provide a. means for frictionally lockingthe shaft 42 against inadvertent rotation. This is simply accomplishedby providing complementary frusto-conical surfaces fixed with respect tothe shaft 42 and with respect to the base 20, such surfaces beingarranged in concentric relation with respect to the shaft 42 and sodisposed that the axial force applied to the shaft 42 when a clampingpressure is applied therethrough to a piece of work in the fixture drawssuch conical surfaces into frictional engagement with each other.

The above-described arrangement may be carried out in a number ofdifferent ways, but in the construction illustrated in Figs. 1 to 6inclusive, the shaft 42 has formed on that end thereof adjacent theoperating lever 48 a frusto-conical surface 52, the small end of suchsurface being disposed inwardly of the corresponding end of the shaftinasmuch as the angularity of the teeth on the pinions 44 and racks 46is such as to tend to move the shaft 42 in such direction upon theoccurrence of resistance tending to prevent downward movement of theclamping plate 24 during the corresponding rotational movement of theshaft 42.

The corresponding end of the corresponding bearing boss 40, which isshown formed integrally with the base 20, is formed with a complementaryfrusto-conical surface 52 so that when such resistance to rotation ofthe shaft 42 occurs through the clamping plate 24 engaging a piece ofwork such as 28 and resulting in a force set up axially in the shaft 42tending to move it to the left as viewed in Fig. 1, the frusto-conicalsurface 52 is drawn into engagement with the surface 54 by a force, asabove explained, proportional to the clamping force applied to the work26, and thus the surfaces 52 and 54 are drawn into firm frictionalengagement with each other.

It will be appreciated, of course, that regardless of the angularity ofthe frusto-conical. surfaces 52 and 54, such frictional engagement willoccur between them under the above-stated conditions, and that evenwhere the-surfaces 52 and 54 have an included angle of degrees, that iswhere they lie in the surface of a plane, such frictional engagementwill be set up and may be sufficient to lock the shaft 42 .under suchcircumstances against such inadvertent rotation in a reverse directionas would release the clamping effect on the work. It will also beappreciated that the sharper the angle of the frusto-conical surfaces 52and 54, the greater will be the frictional engagement between them, butit will also be appreciated that the angularity of these surfaces willpreferably be greater than the angle of friction of the material fromwhich they are formed so that they will not remain together in theabsence of axial pressure tending to maintain their locked position.Preferably the angularity of the surfaces 52 and 54 is such as toapproach but to be materially greater than the angle of friction of thematerial from which they are formed so as to obtain a maximum frictionallocking effect between them upon the application of the abovedescribedaxial pressure on the shaft 42 during .ing plate '48 and knob or ball56, the

2,370, ear

a clam-ping effect on work, andyet provide a construction that does notrequire the application of a force in the opposite direction toseparate. such surfaces and thusto provide one which will automaticallyrelease as scenes the axial pressure is released.

Accordingly, with the above-described construction it will-beappreciated that in practice, a piece of work such as 2.6 is placed onthe table- 22 when the clamping. plate 24 isin elevated position, andthen the workman grasps ,the knob 56 of the operating lever 48 and turnsthe shaft 42 in a direction to lower the clamping plate-24. Under suchcircumstances, as soon. astheclamp- 24 comes in contact with the work 26and the workman applies a material turning force on the shaft 42through-the handle orlever clamping plate 24 will be drawn, down firmlyon the work 26 to clamp it to the table 22 and at thesame time theoperating shaft 42. will move or tend to move axially and will bringthefrusto-conical surfaces 52 and 54 into intimate and frictionallylocked relationship with respect. to each other. This will maintaintheshaft 42 inits then rotatedposition and through it maintain theclamping plate 24 in clampingrelation .with..respect to the work 26 uponrelease of the turning force on the shaft 42, and will hold the shaft 42against inadvertent rotation in the opposite direction. practice it hasbeen found thatparticularly where the knob 50 is made of sumci'ent sizeandmass, after the work .26 has been properly applied to the table 22,the workman may simply throw the knob 56 downwardly and the inertia ofthe same acting through the shaft 412 and posts 28 will be sufiicient tofirmly clamp the work'26 in position and to lock the shaft '42 againstinadvertent rotation in a work loosening direction.

When the machiningoperation on'the work 26 in the clamping fixture thusdescribedhas been completed, the workman simply grasps the knob 50' androtates the shaft 42 in a, direction opposite to that required for theclamping movement of the shaft 42 in the reverse direction immediatelyreleasing the surfaces .52 and 54 from'frictionaI engagement with eachother, this being true not only because such initial movement has theeffect of relieving the above-described axial force on the shaft 42, butdue tothe force transmitted between the pinions 44 and rack 46 necessaryto lift the weight of the clamping plate 24 and post 28, actuallyreversing the directionv of force acting through the shaft 42 to thuseffect a separation of the surfaces 52 and54.

In order to prevent the surfaces 52 and 54 from being separated fromeach. other to an excessive degree during the last-mentioned movement ofthe shaft 42, the end of the shaft 42. opposite the cone 52 thereon isprovided with an axial threaded bore therein in which a screw 6611sreceived and a washer 64 is interposed between the head of the screw andthe corresponding end of the corresponding bearing boss 40, preferablywith the interposition of a lock washer 62. As best brought out in Figs.1 and 3 the Washer 64 is sheared to provide a pair of radially-directedtongues 66 thereon having free inner ends which are inwardly bent asillustrated in Fig 1 into a diametrical slot 68 formed inthecorresponding end of theshaft 42. to thus lock the washer .64 againstrelative rotation with respect to the shaft 42. Therelation of thepartsis such that a slight axial movement oftheshaft-fl ispermitted butIn actual 4215 turned to raisethe the shaft is restricted against anundue-amount of axial movement thereby.

As best brought out in-Fi-g. 1, in ordertoprevent the possibility of theshaft :42 :being turned in a reverse directiontc an extent whichzwouldpermit inadvertent :disengagemenhof the pinions 44 and racks .46,azwasher 1.0 of slightlygreater diameter than the dianieter-ofrthepostsx28 is. secured toithe'bottom end of each post'28 by means of ascrew 12. The shaft 42 may, therefore, be turned to raisethe posts 28until thewashers .16 strike the-lower ends of'the bosses '38which thuslimits further upward movement of the post 28 at a point where thepinions 4'4 and racks46 still remain in meshinglengagement witheachother. Preferably the' posts 28 have a sufficiently-free slida-bleengagement in theibosses 38 thatthey-will dropiunderthe force of gravityif not restricted,

so that when the shaft 42 is turned to'lower'the clamping plate 24, noactual axial force onthe shaftfl will 'be setup tendingtozforcethesurfaces 52 and 54 in 'frictional engagement with each other until theclamping plate-24 contacts the work 26. On the other hand when theshaftclamping plate245it will be appreciated that there will be some axialforce applied to the shaft not only tending to separate the surfaces52'and54, butitending tovbring the Washer 64 intofrictional engagementwith'the corresponding :end of the corresponding bearing boss 41!.-However,theforce applied to the shaftf42 under such circumstancesis notsufficientto exe-rt any material retarding force on therotati'on of theshaft-42.

In some instances, and particularly for-some typesof work the clampingplat-e524 may'rbe of such size and configuration as to be relativelyheavy and in fact'of such mass'that unless otherwise guardedagainst-pressure must'be applied to the lever 48 to prevent it frommoving underthe force of gravity towards its lowermost position. Suchcondition -is-dangerous for the reason. that a Workman may-get hisfingers caught between the clamping plate and thework when the clampingplate 24-thus drops, :unless extremecareis taken. In such cases'the'constructionshown in Figs. 1 to: 6-inclusive, may be'readily modifiedto prevent the possibility of such occurrence,.and the manner ofaccomplishingztlris is'illustratedin. Figs. 17' and'8. isaccomplishediby removing the sorewsfifl andwashers '62and64, and inplace ofsuch vwashers-a; block memberzflfl applied ;.to thecorresponding end-of-thetcorrespondmg; bearingtboss-fll. This block, asbro-ught'out in Fig. 8, has a-straight. loweredgeBZ, and thecorresponding endofthe-table -22iis :formed topro-videa complementarystraight --shoulder '84 which is. also brought out in Fig. :1. Theinter-engagementof these shoulders prevents relative rotational move--mentor thieblockmember 80 with respect to the baseef the-fixture.Thebloek .80..is provided with opening :86 therein concentric with the.axis of the shaft 42-, thissurfacebeingfrusto-conical and taperinginwardly. A screw 88 replaces thescre-W 6.6 and in this .case is of. a,greater length and receivesrthereon azfrusto-conicalmember 96, theperipheral surface of which is complementary to the surface 660i theblock 8,6. The member 9.6 is provided with a pair of axial projections92 thereon which interfit-withithe slotfiilin-thecon responding end-oftheishaft 62 to-thus; hold-the cone. member 8&1 againstrelative rotationwith re spect to the: shaft 'I.helrelation of thepartsfifland-90ris'such thatwherr therscrewHistightened up,, the same limitedamount of raxial movement of the shaft 42 relative to the base, as inthe firstdescribed construction, is provided. With this constructionwhen the clamping plate 24 is raised to release the work 26 between itand the table 22, the posts 28 are raised until the washers contact thebottom ends of the bosses 38, and the application of a turning force tothe shaft 42 is continued, with the result that due to the sameangularity between the teeth of the pinions 44 and racks 40 that causesthe locking action of the shaft to the base upon downward movement ofthe clamping plate 24, the shaft 42 has an axial force applied theretowhich draws the cone member 90 into firm frictional engagement with theconical surface 86 of the block member 80 to thus frictionally lock theclamping plate 24 against inadvertent movement in its raised position.Thus the axial movement of the shaft 42 occurring when an appreciableturning force is applied thereto against resistance is utilized not onlyto lock the parts in their clamping relation, but also to lock the partsin their released relation and this in an extremely simple andeconomical manner.

' It will be appreciated, of course, that coned surfaces equivalent tothe surfaces 52 and 54 may be provided by modifying the constructionthus far shown and described in a number of different ways. Forinstance, in the construction illustrated in Fig. 9, instead of usingthe coned surfaces 52 and 54 at one side of the fixture, these areeliminated, and the opposite end of the operating shaft, hereillustrated at 42a, is formed with a frusto-conical end I00. Thecorresponding end of the corresponding bearing boss, here illustrated at40a, is extended and internally formed to provide a complementary conedsurface I02. The structure otherwise being identical to that firstdescribed, it will be appreciated that the frustoconical surfaces I00and I02 function in identically the same manner as the surfaces 52 and54 of'the first-described construction.

In Fig. 10, in which parts equivalent to the first-describedconstruction are illustrated by equivalent numbers bearing thesub-letter b, the conical surfaces are provided at the same end of theshaft 42b as in the first-described construction, but in this case thatend of the bearing boss 40b in which the conical surface 54 is providedin the first-described construction is in this case formed to provide anexternal conical surface Il0 concentric with the axis of the shaft 42band in this case the member I I2, fixed to the shaft 42b as by means ofa key H4. is formed to present an internal frusto-conical surface IIBarranged for complementary engagement with the surface H0. The operatinghandle or lever 48b serves to limit outward movement of the member I I2on the shaft 42b and a nut Il8 locks the operating handle 48b againstoutward displacement on the shaft 421). It will be appreciated that thismodified structure operates in substantially the same manner as thestructure first described.

In Fig. 11 in which parts equivalent to the firstdescribed constructionare indicated by the same numerals bearing the sub-letter c, theoperating shaft 42c in this case has fixed to the right-hand endthereof, as viewed in Fig. 11 and which figure corresponds to the viewin Fig. 1, a frusto-conical member I20, but in this case instead oftapering inwardly as in the first-described construction, the member Iis tapered outwardly or to the right as viewed in Fig. 11. In order toprovide a complementary cone surface such as I22 for the member I20, aseparate member I24 is provided in this case and secured to thecorresponding end of the base portion of the fixture by screws I25. Inthis case, in order to utilize the conical surfaces for locking thefixture in its clamped position, it is necessary that the hand of theteeth of the pinion 44c and the rack 460 be reversed from that shown inthe preceding views so that when the final clamping pressure is appliedto the shaft 420 an axial component of force is applied to the shaft 420acting to the right as viewed in Fig. 11, instead of to the left as inthe previously described constructions. Otherwise the construction isthe same as in the first-described construction and functions inidentically the same manner.

InFigs. 12 and 13 another modified form of construction is shownrespects to the construction first described, and for that reasonequivalent parts are indicated by the same numerals. except that inFigs. 12 and 13 such numerals bear the sub-letter d. Accordingly, onlythe differences between the two constructions need be specificallymentioned. The base 20d is substantially the same as the base 20 firstdescribed, except that the table 22d thereof is of slightly greaterheight and instead of employing a pair of bosses such as the bosses 40first described for receiving the shaft 42, a single transverse boss 40dis provided for rotatably receiving the operating shaft 42d. The base20d is also provided with a pair of laterally spaced verticallyextending hollow bosses 38d corresponding to the bosses 38 firstdescribed and in each of which a post 28d, corresponding to the posts 28first described, are vertically slidably received but in this casetheposts 28d are positioned a sufficient distance forwardly of theoperating shaft 42d as to be entirely out of contact therewith.Accordingly, the posts 28d simply serve as guides for the clamping plate24d in its vertical movement relative to the table 22d and are notformed to provide racks thereon.

In order to raise and lower the clamping plate 24d, a third verticallyextending boss I30 is provided on the base 20d midway between the bosses38d and offset rearwardly therefrom. The boss I30 slidably receivestherein a post I32 arranged with its axis parallel to the posts 20d. Theupper end of the post I32 is reduced to the same diameter as the .upperthreaded ends of the post 28d so as to provide a shoulder abutting thelower face of the clamping plate 24d through which it projects, and anut 32d, the same as the nuts 32d on the posts 28d, is threaded on theupper end of the same to hold it against relative axial movement withrespect to the clamping plate 24d.

The surface of the post I32 is arranged in intersecting relationshipwith respect to the surface of the shaft 42d, and the shaft 42d isformed to provide a helical pinion 44d thereon at such point ofintersection, and the post I32 is formed to provide a rack 46d inmeshing engagement therewith. Thus in this case the posts 28d servesolely as guides in the movement of the clamping plate 24d, and althoughthe post I32 also serves in the nature of a guide post, its primarypurpose is that of providing a connection between the operating shaft42d and the clamping plate 24d to effect raising and lowering movementsthereof. Thus although a multiple post fixture is provided, only one ofthe posts is required to be machined to provide the rack 45d thereon,and only one pinion 44d is required to be provided on the operatingwhich is similar in many shaft AM. The structure may, therefore, beslightly more conomical to build than the construction first describedbut without detracting from the rigidity of the same.

The operating shaft 4211 is provided with a frusto-conical surface 52dthereon cooperating with a complementary frusto-conical opening 54d inthe right-hand end of the boss 40d as viewed in Figs. 12 and 13, and inview of the fact that the pinion Md and rack 46d are of the same generalhelical conformation as in the construction first described, operate tofrictionally lock the fixture in clamped relation in substantially thesame manner as the construction first described. One thing to be notedin connection-with the construction illustrated in Figs. 12 and- 13 isthat the operating shaft lZcZ is made from a cylindrical piece of stockof a diameter equal to the maximum diameter of the frusto-conicalsurface 52d and that end thereof outwardly of the surface 52d is allowedto remain at its full diameter and is provided with a diametrical holetherethrough in which one end of the handle or lever'member 48d isremovably received and fixed against movement by means. of a set screwI34 into the outer end of the operating shaft 42d.

The end of the boss 40d opposite that at which the frusto-conicalsurface 5411 is located is formed directly to provide a frusto-conicalsurface I36 identical in size and shape to the surface 54d but simplyreversed in direction therefrom. This is in lieu of providing a separatemember such as the member 8'?) in the modification shown in Figs. 7 and8. The corresponding end of the operating shaft 42d is reduced indiameter and threaded to provide a stud 42d upon which concentricfrusto-conical member I38 is received.

The cone member is prevented from relative rotation on the stud 42d bymeans of a diametrical key MS, of the same width as the stud 42d andformed by straddle milling the end of the shaft 42d except for the widthof the stud 42d. The small end of the cone member I 38 is diametricallyslotted as at M1 for reception of the key MEI. Clearance is providedbetween the outer end of the key I40 and bottom of the slot I4I so thatany wear between the cone member I38 and the surface I36 will beautomatically taken up. Lock nuts Hi2 threaded on the lefthand end ofthe operating shaft 42d together with-a washer I l-ii serves to limitoutward movement of the cone member I38 on the shaft 42d. In thisconstruction the cone member I38 is provided with a counterbore I46 inits outer end within which is received a. coil compression spring I41surrounding the outer end of the operating shaft 42d and maintainedunder compression between the bottom of the recess and the washer I44 soas to constantly urge the cone member I 38 inwardly into engagementwiththe frusto-conical surface 36. The spring MB is relatively light andits only function is to constantly maintain the cone member I33 incontact with the surface :36 and so as to insure a small amount offriction being set up at this point at all times. The function of thecone member I38 is the same as that of the cone member 80 in connectionwith Figs. '7 and 8, that is to provide a friction lock between theoperating shaft and the base d when any material resistance is exertedtending to prevent upward movement of the clamping plate 24d and toprevent inadvertent movement. of the clamping plate 42d downwardly underthe force of gravity. In other words, it is a safety feature designed toprevent the clamping plate 2412 from dropping of its own accord andpossibly catching the fingers of aworkmanbetween it and :work beinginserted into or'removed from the fixture. It will be noted particularlyfrom an inspection of Fig. 12 that the large end of the cone member I38has a cylindrical portion I48 formed thereon and that .the outer end ofthe conical opening I36 is provided with a cylindrical bore portion I49complementary thereto and in which the portion I48 is relatively closelyreceived. The cone member 52d is similarly formed as. illustrated inFig. 13 This construction is preferably used for all the equivalent conemembers shown in the various modifications and is for the purpose offorming a seal to prevent dust or dirt from entering between thecooperating coned surfaces. It will be appreciated that with thisconstruction although the cone member I38 may withdraw axially from itscooperating cone socket portion I35 in the base the .close clearancebetween the cylindricalend I48 and the cooperating surface'I lQ willremain constant and thus provide an effective seal.

- In view of the fact that the frusto-conical surfacesfidd. and I36 areidentical to each other, and because of the fact that the pinion 44d islocated midway between the opposite sides of the boss Mid, it will :beappreciated that the operating shaft 42d may be assembled from eitherside of the fixture and that the cones 52d and I38 in being reversedtherewith will operate in identically the same manner as abovedescribed. By this means the shaft 42d maybe reversed with the handle48d and thus permits the fixture to be used as either a righthand-orlefthand fixture as may be desired; in any case. There may be instanceswhere it is desired to introduce a yielding element between theoperating shaft and the clamping plate of a clamping fixture such as anyone of the structures above described. This is particularly so where thework to be operated upon is a casting having a relatively rough surfacegripped between the clamping plate and the table, as insuch case thepressure may be exerted against a small number of relatively roughpoints on the work which may break down during the machining operation.Under such circumstances if the clamping plate is not capable offollowing downwardly to take up the clearance which would otherwise beestablished by breaking down of the rough point, the work may becomeloosened in the fixture. Such yieldability may be introduced between-theoperating shaft and the clamping plate in the manner illustrated in Fig.14, and may be applied to any of the constructions above described byreplacing the nut 32 at the upper ends of the posts 28 by the same. Inthe construction illustrated in Figs. 12 and 13 it may be employed toreplace the nut 32d on the central post I32, to obtain the same results.

In Fig. 14 the clamping plate is illustrated at Zde and may be identicalto any of the clamping plates heretofore described. The post 28a asabovedescribed may be the same as any of the posts 28 previously described inFigs. 1 to 11, inclusive, or may be the post I32 described'in connectionwith Figs. 12 and 13. In place of the nut'32 or its equivalent'which isremoved in such case a relatively long sleeve-like nut I50 is threadedonto the upper end of the post 28a in its place. Before threading on thenut I50 a sleeve I52 having an inturned lowerend I54is slipped over theyupper end of .the post 28c, followed by a coil compression spring I56within which the nut l50 is projected. The nut I50 adjacent its upperend is provided with an annular radially outwardly directed flange I58which is axially slidably received within the open upper end of thesleeve I52 and in threading the nut I50 downwardly on the post 28c thespring I56 is compressed between the flange I58 and the flange I54 ofthe sleeve I52, thus acting to urge the clamping plate 24e downwardly onthe post 28c against its cooperating shoulders on the post. To lock thenut I50 against movement on the post 286, a clamping plug I60 isthreaded downwardly into the bore of the nut I50 and into bindingengagement with the upper end of the post 28c.

. With the above described construction it will be appreciated that whenthe operating handle or lever 48 is operated to force the clamping plate24c downwardly against a piece of work, if sufficient force is appliedit will cause the spring I56 to be compressed, the clamping plate 24cwill move upwardly on the post 28e'away from the cooperating shoulder onsuch post, and the clamping force on the work will in reality be takenthrough the spring I56. This spring is relatively heavy and, of course,designed to exert a sufficient amount of clamping force on the Workthrough it to hold the work in position in the fixture. Assuming that apiece of work is clamped in the fixture through the spring I56 and thespring I56 has been compressed a material extent during the clampingoperation, it will be appreciated that if any rough points on the workshould break off during the machining operation the force of the springI56 will automatically cause the clamping plate 44 to move downwardly tocompensate for such points that are broken off and so as to maintain arequired amount of clamping force on the work regardless of suchoccurrence. It will also be appreciated that Where such a resilientelement is desired in any fixture of the type described the only changein the fixture is replacement of the nut or nuts at the upper end of theposts 28 in the constructions shown in Figs. 1 to 11 and the post I32 inFigs. 12 and 13, by the structure illustrated in Fig. 14 to obtain thedesired result.

The method of securing a handle or lever 48d to the operating shaft 42din Figs. 12 and 13 is p rhaps. more desirable than the constructionshown in the preceding views for the reason that it permits substitutionof different types of handles with greater ease than with theconstruction first described. For instance, there may be some caseswhere it is desirable to employ a long operating handle or lever onlyduring a clamping or an unclamping operation and to provide no handle atall or only a short piece of a handle during a machining operation. Insuch case a construction such as illustrated in Fig. 15 may be resortedto.

Referring to Fig. 15 it will be noted that instead of employing a longhandle such as 48d in Figs, 12 and 13, such handle is replaced by arelatively short bar I64 having a tapered or frusto-conical end portionI 66 projecting from the operating shaft 42d. In this case a relativelylong handle or lever member I68 which is provided with a socket I in oneend thereof complementary to the end I66 is removably received on theend I66. The handle or lever I68 may thus be app-lied to or removed fromthe end I66 as the occasion may demand.

Another form of handle construction is illustrated in Fig. 16 for use insubstantially the same instances as the construction shown in Fig. 15 isused in. In this case instead of an elongated handle or lever membersuch as 48d, a relatively short pin I12 is inserted in the end of thoperating shaft 42d and secured in place by the set screw I34 withitsvopposite ends projecting a short distance radially beyond the outersurface of the operating shaft 42d. An end wrench I14 having a socketend I16 of a size to receive the outer end of the operating shaft 42dtherein is provided in this case, and the socket end I16 is providedwith a plurality of diametrically opposed sets of slots I18 extendingaxially of the op n end thereof, the slots I18 being of a sufficientwidth to receive the projecting ends of the pins I12 therein. The wrenchI14 is provided with a cross-handle I for the purpose of enabling it tobe manually turned. It will be appreciated that in this case the pin I12 projects a minimum distance radially outwardly from the correspondingend of the operating shaft 42d and the wrench I14 may be applied to itin any one.

of a plurality of angular positions for the purpose of turning the shaft42d and may be readily removed as soon as the clamping fixture is eitherpositioned in clamped or unclamped position. This last form ofconstruction is particularly desirable for use where such clampingfixtures are mounted on a rotating table of a machine tool for differentoperations at differ nt angular positions of the same.

In all of the constructions thus far described the helical pinion orpinions have been shown and described as being fixed with respect to theoperating shaft and the shiftable frusto-conical member formed as afixed :part of the operating shaft. While this may be preferable in mostinstances as constituting the most economical way of obtaining thedesired result, it is not at all essential. For instance, and asillustrated in Fig. 17, the conical surface is formed as part of thepinion, and although the pinion in such case may be either fixed to ormovable axially of the operating shaft,- as a matter of illustration itis shown mounted for relative axial movement on the operating shaft andmovement of the pinion rather than the shaft is relied upon to effectthe frictional locking feature of the fixture.

In Fig. 17 parts equivalent to the construction previously described areindicated by the same numerals except that such numbers bear thesubletter The post 28f in Fig. 17 is equivalent to the posts 28previousl described and is formed to provide a rack 46 thereoncorresponding to the rack 46 previously described. In this case theoperating shaft 42 is simply a cylindrical member to one end of which anoperating handle I is non-rotatably secured by means of a key I92 andnut I94. The helical pinion 44f, instead of being formed integrally withthe shaft 421 as in the previously described constructions is, in thiscase, formed separately and is secured on the shaft 42f for relativeaxial movement with respect thereto, but against relative rotation withrespect thereto by means of a key I96. One end of the pinion 44 isextended and is formed to provide a frusto-conical surface I98 thereonconcentric with the axis of the shaft 42f. The cooperating boss 40) isinternally formed to provide a complementary frusto-conical surface 200.Movement of the pinion 44f away from the surface 286 is limited by meansof a collar 202 fixed to the shaft 42 bymeans of a pin 204. With thisconstruction it will be appreciated that when a clamping forceis exertedthrough the handle or lever 19!! on the operating shaft 421, such forceis transmitted through the pinion 44 to the rack 46 and when such forceis built up due to the clamping effect of the fixture on a piece ofwork, then thereaction between the teeth of the pinion 44 and rack ittends to shift the pinion Ali to the left as viewedin Fig. 17 and forcethe frusto-conical end I38 of the pinion into frictional lockingengagement with the frusto-conical surface 2% formed in the boss 40 ofthe base, thus resulting in identically the same locking effect as inthe constructions previously described.

Having thus described my invention, what I claim by Letters Patent is: s

1. In a clamping fixture of the'class wherein there is a base, aclamping member is guided for movement toward and from said base andadapted to clamp a piece of work between it. and said base, a rack partis secured to said clamping member through which movement of saidclampingmember toward and from-said base is effected, a-pinion part isprovided in meshing relation with respect to said rack part foreffecting movement of said rack part in a clamping direction, anoperating shaft part is drivingly connected to said pinion part foreffecting rotation thereof,

and a handle part is drivingly connected to said shaft part for effectinrotation of said shaft part, the combination with said base and two ofsaid parts of a connection between said two of said parts includingco-operating surfaces operative upon the transmission of a materialforce to said clamping member tending to move it relative to said baseto shift one'of said two parts laterally of the direction of movementthereof required to effect, movement of said clamping member relative tosaid base, a pair of co-operating friction surfaces one fixed relativeto said base and one shiftable laterally upon lateral shifting of saidone of said two parts engageable with each other under the influence ofa clamping force transmitted between said handle part and said clampingmember to frictionally lock said clamping member against inadvertentmovement away from said base, and a second pair of co-operating frictionsurfaces one fixed relative to said base and one shiftable laterallyupon lateral shifting of said one of said two parts en'- gageable witheach other under the influence of a force exerted between said two ofsaid parts in a direction opposite to the direction of said clampingforce exerted therebetweento frictionally lock said clamping memberagainst inadvertent movement toward said base.

2. In a clamping fixture of the class wherein there is a base, aclamping member is movable toward and from said base, a post is securedto said clamping member and axially slidably received by said base, ashaft is rotatably mounted on said base transversely of said post; andmeans are provided in each instance for rotating said shaft, thecombination with said base, post, and shaft of a part providing afriction surface fixed with respect to said base, apart providing asecond friction surface complementary to. the first '3. In a clampingfixture of the class wherein there is a base, a clamping member ismovable toward and from said base, a post is secured to said clampingmember and axially slidably received by said base, a shaft is rotatablymounted on said base transversely of said post, and means are providedin each instance for rotating said shaft, an axially shiftable piniongear rotatable by said shaft, rack teeth on said post arranged inmeshing relationship with said pinion gear whereby rotation of saidshaft is accompanied by axial movement of said post, a part having aconed surface fixed with respect to said pinion gear for equal rotationtherewith and for equal axial movement in at least one direction, saidbase having a part providing a frusto-conical surface complementary tothe first mentionedfrusto-conical surface, said pinion gear havinghelically arranged teeth thereon of such hand that upon the presence ofa material pressure between said teeth' and the teeth of saidrack saidpinion is caused to move axially to effect interengagement of said conedsurface.

4. In a clamping fixture of the class wherein there is a base,'aclamping member is arranged in co-operative relation with respectthereto, and means are provided in each instance for effecting relativemovement between said clamping member and said base comprising a rackmember fixed with respectto said clamping member, a pinion rotatablysupported on said base in meshing relationship with respect to said rackmember, and means for rotating said pinion, the combination with saidbase, pinion and rack member ofhelically arranged teeth on said pinion,angularly arranged teeth on said rack member in meshing engagement withsaid teeth of said pinion whereby a rotative force applied to saidpinion tending to move said rack means against resistance tends todisplace said pinion axially thereof, and complementary frictionalsurfaces one fixed with respect to said base and the other rotatably andaxially movablewith said pinion engageable with each other uponsaidaxial shift- "ing of said pinion to frictionally lock said pinionagainst inadvertent rotation with respect to said base. I

5; In a clamping fixture of the class wherein a clamping member ismovable toward and from a 'base, the combination with said clampingmember and base of a post fixed to said clamping member and slidablyreceived by said base, a helical pinion gear rotatably mounted on saidbase about an axis disposed transversely with respect to said post, saidpinion gear being mounted for axial shifting movement, rack teeth fixedwith respect to said post-arranged in meshing relation with respect tosaid pinion gear, means for rotating said pinion gear, said base havinga friction surface fixed with respect thereto, and a part secured tosaid pinion for movement in the direction of shifting movementtherewithand arranged for frictional engagement with said friction surface onsaid base'upon'axial shifting of said pinion in a direction to effectengagement of said part and friction surface, the angularity of theteeth.

of said gear andrack being such as to effect axial movement ofsaid'pinion in said direction under the influence of a force exertedbetween said pinion gear and said rack teeth when a workpiece is clampedagainst said base by said clamping member.

6. In a clamping fixture of the class wherein there is a base, aclamping plate is relatively movable With respect thereto, a post isfixed to said clamping plate and slidably received by said post, and ashaft is rotatably mounted on said base with its axis disposedtransversely to the length of said post, the combination with said base,post, and shaft of a helical pinion gear mounted on said shaft, rackteeth on said post in meshing engagement with said pinion gear, saidpinion gear being axially shiftable under the influence of a forcetransmitted therethrough to said teeth on said post to move the latteragainst a resistance, said base having a frictional surface fixed withrespect thereto in surrounding relation with respect to the axis of saidshaft, and a complementary frictional surface movable with said pinionaxially thereof into frictional locking engagement with the firstmentioned frictional surface upon axial movement of said pinion in onedirection, the angularity of the teeth of said gear and rack being suchas to effect said axial movement of said gear under the influence of aforce transmitted through them in the clamping of a workpiece againstsaid base by said clamping plate.

7. In a clamping fixture of the class wherein there is a base, aclamping member is movable toward and from said base, a post is securedto said clamping member and slidably received by said base, and a shaftis rotatably mounted in said base in perpendicular relationship withrespect to said post, the combination with said base, post, and shaft ofa helical pinion fixed to said shaft, rack teeth on said post arrangedfor meshing relationship with respect to said pinion gear, said shafthaving a limited amount of axial movement relative to said base, saidshaft having a coned surface thereon, said base having a complementaryconed surface thereon arranged for frictional locking engagement withsaid coned surface of said shaft upon axial movement therewith saidbase, and a shaft is rotatably mounted in said base in perpendicularrelationship with respect to said post and having a limited amount ofaxial movement in said base, the combination with said base, post, andshaft of a spiral pinion gear fixed to said shaft, said post having acomplementary rack thereon whereby rotation of said shaft acting throughsaid pinion, rack and post effects movement of said clamping membertoward and from said base, a cone member fixed concentrically withrespect to said shaft, said base having a surface complementary to theconical surface of said cone member and arranged for frictional lockingengagement therewith .upon axial movement of said shaft in one directionunder the influence of a clamping force exerted between said pinion andrack, a second cone element fixed with respect to said shaft and taperedaxially of said shaft in a direction opposite to the taper of the firstmentioned cone element, and said base having a complementary conesurface fixed with respect thereto complementary to said second coneelement and adapted for frictional locking engagement therewith uponaxial movement of said shaft in a direction opposite to the firstmentioned axial movement thereof against a material resistance.

9. In a clamping fixture of the class wherein there is a base, aclamping member is movable toward and from said base, a plurality ofposts are fixed with respect to said clamping member and slidablyassociated with said base, rack teeth are formed on said posts, a shaftis rotatably and axially mounted in said base, and a plurality ofpinions are fixed with respect to said shaft and each arranged inmeshing relation with respect to said rack teeth on the corresponding ofsaid posts, the combination with said base, posts, shaft and pinions ofa part having a coned surface concentric with the axis of said shaftfixed with respect thereto, a part having a coned surface complementaryto the first mentioned frustoconical surface fixed with respect to saidbase, and frictionally interengageable therewith upon axial movement ofsaid shaft in one direction, at least one of said pinions havinghelically arranged teeth thereon and being axially shiftable relative tosaid base and the corresponding of said rack teeth on the correspondingof said posts being disposed at an angle to both the length and width ofsaid posts for meshing relationship therewith, the angularity of theteeth of said one of said pinions and the angularity of said rack teethbeing such as to effect said axial movement of said one of said pinionsunder the'infiuence of the force transmitted through them in theclamping of a workpiece against said base by said clamping member.

10. In a clamping fixture of the class wherein there is a base, aclamping member is movable toward and from said base, a pair of postsare secured to said clamping member in parallel relation with respect toeach other and slidably received by said base for guiding said clampingmember in its movement with respect to said base, a third post is fixedto said clamping member in parallel relation with respect to the twofirst mentioned posts, and a shaft is rotatably mounted in said base,the combination with said base, shaft and third post of a. helicalpinion mounted on said shaft for receiving driving movement therefrom,complementary rack teeth formed on said third post in meshingrelationship with respect to said pinion, means providing a frictionsurface shiftable axially of and with said shaft with respect to saidbase, a complementary friction surface fixed with respect to said base,means in the connection between said shaft and said third post operableto effect axial shifting movement of the first mentioned frictionsurface upon the transmission of a material force between said shaft andsaid third post whereby to effect frictional engagement of saidfrictional surfaces, and means for rotating said shaft.

ERNEST F. HOHWART.

